Liquid crystal display devices are display devices that use a liquid crystal composition for display. A representative display method therefor is one in which the light transmission amount is controlled by applying a voltage to the liquid crystal composition sealed between a pair of substrates to change the orientation state of the liquid crystal molecules in the liquid crystal composition according to the applied voltage. Such liquid crystal display devices exploit advantages such as being thin, lightweight, and exhibiting low power consumption, and are used in a wide range of areas.
When voltage is not being applied, the orientation of the liquid crystal molecules is generally controlled by alignment films formed on the surfaces of the substrates. Conventionally, polyamic acid and polyimides have been widely used as the material for the alignment films (liquid crystal orientation agent). Among organic resins, polyamic acid and polyimides exhibit excellent physical characteristics in areas such as durability against heat, an affinity for liquid crystal, and mechanical strength. However, as the number of applications for liquid crystal panels increases and the usage environment becomes more diverse, a material with even better durability against heat has been sought after. An alignment film that uses a polymer with a polysiloxane as the main framework has been proposed (see Patent Documents 1 and 2, for example).
Patent Document 1 discloses a vertical alignment film having a siloxane structure and a thermal crosslinking group (epoxy group) that uses an alignment film material containing a liquid crystal orientation side chain having a carbon-carbon double bond that is bonded to silicon, thereby improving vertical alignment and reducing unevenness resulting from the liquid crystal dripping step.
Patent Document 2 discloses a liquid crystal orientation agent containing at least one type selected from a group including a polysiloxane having a side chain of a specific structure in a repeating unit, a hydrolyzate thereof, and a hydrolyzate condensate, and containing a reaction product with a specific compound. Patent Document 2 also discloses that the liquid crystal orientation agent may further contain at least one type selected from a group including polyamic acid and a polyimide, and that the liquid crystal orientation agent is used in a liquid crystal display element.
As a method of filling the liquid crystal panel with liquid crystal, the vacuum injection method and the one drop fill (ODF) method are widely known. The vacuum injection method relies on capillary action and injecting liquid crystal into a large display such as a television receiver or signage, in particular, but this method requires a considerable amount of time, and it is especially difficult for liquid crystal to spread in a vertical alignment liquid crystal panel, which has made it very difficult to introduce the liquid crystal. Thus, the ODF method has been in primary use when manufacturing large substrates/panels. FIGS. 15 and 16 are for describing ODF. FIG. 15 shows a state in which liquid crystal droplets are dripped onto one substrate, and FIG. 16 shows a state in which the pair of substrates are bonded together in a vacuum and the liquid crystal droplets spread under pressure across the entire surface of the substrates. As shown in FIG. 15, by the ODF method, after a necessary amount of liquid crystal droplets 31 is dripped onto prescribed locations on one substrate on which an alignment film is formed, the other substrate is bonded to the one substrate in a vacuum and the liquid crystal droplets 31 are spread under pressure throughout the entire surface of the substrates as shown in FIG. 16, and the surrounding sealing member is cured by ultraviolet light, heat, or a combination thereof, thereby filling in the space to the inside of the sealing member with liquid crystal.
On the other hand, when ODF was used, this sometimes resulted in a particular type of display unevenness. Specifically, this resulted in uneven display color depending on the position where the liquid crystal droplets were dripped or the shape and pressure when the liquid crystal droplets are spreading. As a countermeasure, by introducing an additive to the polyimide alignment film material, the spread of liquid crystal droplets on the alignment film is facilitated, and this has been proposed as a method of eliminating unevenness when dripping liquid crystal (see Patent Documents 3 and 4, for example). However, because a polyimide alignment film material was used, there was room for improvement in reliability. In addition, in order to reduce unevenness when dripping liquid crystal, a method of further facilitating the spread of liquid crystal droplets on the alignment film has been sought after.